Various control systems have in the past been proposed for mining or tunnelling machines. One such system, for example, is disclosed in International Patent Application (PCT) WO 91/18184 published Nov. 28, 1991. The machine disclosed therein is of a particular type with a large rotatable cutting wheel which is moved laterally as it rotates, thereby cutting a face having a height that essentially corresponds to the diameter of the cutting wheel. The control system of such a machine cannot be readily adapted to boom type mining or tunnelling machines wherein the boom is both tiltable and rotatable to achieve a desired profile of the cut, where "profile" means any path that the boom is directed to take, limited only by the mechanical constraints or the machine.
Other known systems provide for the cutting of a predetermined profile, but without a continuous control of the operation which enables appropriate corrections to be made as the face is being cut and while the machine is operating. Such known control systems are rudimentary in that control of individual movements (e.g. via control of individual hydraulic circuits or electric motors) is done in an essentially open-loop fashion, i.e. although there is some monitoring of the position of sump, boom and turret-rotation, the system is not able to react to that information other than in a discontinuous fashion. For profile cutting, a cam or a particular, simple cam algorithm for a given set of profile dimensions may be used to produce discrete, separate movements of boom and turret at certain distance intervals of movement of one or the other of boom-pivot or turret-rotation; this produces a profile accurate to within one or two degrees of movement of boom and/or turret (of the order of 3-5 cm. at best in terms of the profile itself). The lack of continuous control in known machines results in, not only inaccuracy of position and change of position (movement) in sump, boom-pivot and turret-rotate, but consequent with that inaccuracy, a great potential for variation in the rate of movement through the rock and thus a similar great potential for variation in forces experienced by the cutting head and tools. In hard rock cutting, for example, this lack of continuous and accurate control of position, movement and force results in, at best, an inaccurate profile and a much shortened tool life and, at worst, an almost total inability to penetrate and cut the rock. In very fractured ground, such uncontrolled cutting can also result in undesired blocks of rock being torn or pulled from the perimeter of an excavated opening, thus exacerbating ground control problems. A further disadvantage of the previous systems is that for any change in profile dimensions, an entirely new set of corresponding boom angle and turret angle values would have to be generated externally and then programmed into the machine computing system.
Thus, no satisfactory continuous control system appears to exist for a boom type machine such as mentioned above, wherein the boom is tiltable and rotatable and wherein the cutting head is also rotated using a separate motor or hydraulic drive for that purpose.